In a computer network, network switching devices (switches) interconnect to form a path for transmitting information between an originator and a recipient. A routing mechanism, or protocol, defines switching logic that forwards the transmitted information in the form of packets between the switches as a series of “hops” along a path. At each switch, the switching logic identifies the next switch, or hop, in the path using an identifier such as a MAC address. Shortest Path Bridging (SPB) is a routing mechanism having switching logic such that each switch advertises the nodes it knows about to all the other switches, and eventually all the switches in the network have the same picture of the network and therefore can forward frames to the next hop in the shortest path.
An access network provides connectivity to end stations that provide computing services to users. Typically, an end station communicates with another end station at a remote access network, which may be another user, a server, a storage device, or a gateway to such entities or services. A transport network provides connectivity and message traffic transport between the access networks. The access network is therefore supporting a number of end users via end stations in a corporate site, local area network, or other campus or enterprise setting. Since an interruption of connection between the access network and transport network may inhibit operation of the access network, and hence all end stations connected to it, it is beneficial to provide an alternate mechanism for throughput from the transport to the access network. Configurations disclosed herein provide multiple connections via a plurality of network devices, such as a network switch, from the transport network to the access network. In an example arrangement shown below, a transport network employs a dual homing arrangement to the access network to provide connectivity from multiple network switches.
Dual homing is a mechanism by which an access network connects to and uses a pair of devices in the transport network as if it were connecting to a single device. The two devices (network switches) in the transport network exchange information between them which allow them to present the access network to the rest of the transport network as if the access network was connected to a single device in the transport network. Failure of the connection of one of the transport devices to the access network or even the complete failure of one of the transport devices will not cause loss of connectivity between the access network and the transport network. The access network therefore exhibits dual homed access, which is an access network that uses dual homing to connect to a pair of transport devices, and the transport devices define a dual homed edge, or a pair of partner devices, in the transport network that provide dual homing service to an access network. The disclosed dual homed access configurations, routing logic and deployment are applicable to other multiple homed schemes as well.
In the examples disclosed herein, the transport network is an SPB network. SPB is defined in IEEE-802.1aq: IEEE standard for Shortest Path Bridging, and operates in conjunction with IEEE-802.1ah: IEEE standard for Provider Backbone Bridging, sometimes referred to as Mac-in-Mac encapsulation (SPBM). Shortest Path Bridging (SPB, SPBM) technology is being adopted in Ethernet based data networks to enable Layer-2 and Layer-3 network virtualization. These networks are expected to continue to deliver business critical services even when a variety of network faults occur (or when maintenance operations are performed on the network). Both SPB and SPBM forward packets on shortest path trees with minimum path cost as a first order tie-breaker, where for any pair of nodes A and B, the unicast path for A to B is the exact reverse of the path from B to A (reverse path congruency), and all multicast traffic between the two nodes follows the unicast path (multicast and unicast congruency). These are extensions to fundamental Ethernet forwarding properties in IEEE bridged networks. SPB technology allows a network administrator to easily form mesh networks that distribute load more evenly across the network topology since it can mitigate bottlenecks at core links for traffic that only needs to go from one distribution switch to another.